1. The Field of the Invention
The present invention relates to a projection system and projector.
2. The Relevant Technology
As an apparatus capable of displaying a large screen image, there has been a commercially available projector in which light from a light source apparatus illuminates a small light modulator that forms an optical image in accordance with image information and the optical image is enlarged and displayed through a projection lens on a screen or any other suitable surface.
In recent years, the performance of projectors has significantly progressed. Such high performance owes greatly to an optical system of a projector. For example, an ultra-short focal length optical system and a high magnification optical zooming system allow a user to use a projector more comfortably, and a rigorously designed optical system substantially free of lens aberrations allows the resolution of an image to be increased.
To incorporate more advanced features, it is more difficult to design an optical system that satisfies the requirements. On the other hand, attempts to design an optical system having excellent performance quality tend to end up increase in size of the optical system. As a result, the overall size of a projector increases, which is against market requirements of reduction in size of a projector and hence contributes to decrease in value for customers.
To address the problem, many studies have been conducted on reduction in size of an optical system (see JP-A-2005-157153, for example). In JP-A-2005-157153, a relay system disposed between an image display device (panel) and a projection lens is used to form an intermediate image magnified to be larger than the panel and located on the object side (panel side) of the projection lens, whereby the f-number (an index representing the brightness expressed by the ratio of the focal length of a lens to the diameter of an entrance pupil) is increased. As a result, the back focal length can be reduced, and an ultra-wide angle projection lens is achieved.
The method described above, however, has the following problem: That is, when a relay system capable of displaying a high-definition image is required, a large number of lenses are used to design the optical system, as described in JP-A-2005-157153, probably resulting in an increased length of the overall optical system including the projection lens. Further, an optical system is, in general, designed in consideration of aberrations induced by the lenses used in the optical system, and the design tends to be complicated when the number of lenses that form the optical system increases. When an optical system in question is a telecentric relay system, the design is much more complicated.